The invention relates to a method of producing molded glass bodies in accordance with the press-molding method, and to an apparatus particularly suited for executing this method.
Generally, the methods used for molding glass bodies are those which involve a plurality of press molds disposed with constant angular spacing on a rotatable machine table. After the press mold that is located under a filling apparatus, the so-called feeder, has been filled with a predetermined quantity of molten glass, the table is turned by the angular distance of two adjacent press molds, so that the one now containing the molten glass is positioned under a molding plug. The molding plug, which determines the interior shape of the molded glass body, is lowered into the mold and presses the molten glass into its actual exterior shape. During this procedure, the adjacent press mold, which is now located under the feeder, is filled with molten glass. After the minimum time required to complete the forming of the glass body, which is usually in a range of a few seconds, the molding plug is withdrawn from the press mold, the machine table is rotated again by the angular distance of two adjacent molds, and the cycle starts over.
The completed molded glass body remains in its press mold until it has cooled, through radiant emission and in particular through heat dissipation via the press mold, to the point at which it has solidified into a dimensionally-stable body. Typically, the time required for cooling significantly exceeds the pressing time for completing the molding procedure, so the molded glass body has to be cooled in the mold for the duration of several cycles. Therefore, the machine table must be equipped with at least enough press molds that the time required for transport from the pressing station to an unmolding station at least corresponds to the time required for cooling. The formula for the cooling time t.sub.k is: EQU t.sub.k =(z-1)t.sub.p =zt.sub.T,
where z is the number of cycles, t.sub.T is the pressing time and t.sub.P is the time the rotating table requires to turn by an angular distance corresponding to the spacing between two adjacent molds. The capability of such a method, therefore, does not merely depend on the minimum pressing time required for molding the glass body, but it is substantially limited by the time required to cool the molded glass body until it solidifies.
Hence, a significant disadvantage of the procedure is that the capability of the method cannot be increased significantly, even with the use of more expensive and more efficient pressing drives, which allow for faster molding of the glass body.